Where Web3 Transactions Get Attacked — A High Level Security Breakdown
Welcome back 😆
Last post I walked through what actually happens when you hit "Confirm" on MetaMask which involved the signing, the mempool, execution and finality. The boring plumbing stuff. This one is more fun.
Same four stages. But this time we're looking at each one from the attacker's perspective.
Stage 1: The Wallet — Phishing
The attack starts before your transaction even touches the network.
Here's what most people get wrong, attackers aren't trying to break your cryptographic signature. That math is essentially uncrackable at current compute levels. They're coming for you instead so be aware.
The playbook is simple. They clone a legitimate app — pixel-perfect, same URL structure, sometimes even seeded through official-looking Discord links. You connect your wallet, you read "Confirm transaction," and you click it. What you actually signed wasn't a trade. It was a permission slip, an approve() call that grants their smart contract unlimited access to drain your wallet. Legally, from the blockchain's perspective, you authorized it.
The scariest part? The signature looks identical to a normal one. Most people don't know what they're signing until it's too late.
Stage 2: The Mempool — Front-Running (MEV)
Your signed transaction is now sitting in a public queue. Anyone can see it. That's not a bug - it's how the network is designed. But it creates a very specific problem.
Maximal Extractable Value (MEV) is the term for profit extracted by reordering, inserting or censoring transactions in a block. Front-running is the most common flavor.
Here's how it plays out in practice: you start by submitting a large buy order for a token. An MEV bot spots it in the mempool and calculates the price impact your trade will have. It submits its own buy order with a slightly higher gas fee essentially paying to jump the queue. The bot buys before you, your trade executes at the new higher price then the bot sells into your order. The whole thing happens in one block, sometimes milliseconds.
You paid more than you should have. The bot captured the difference. You didn't notice.
This isn't a fringe attack. MEV bots extracted over $1.3 billion from Ethereum users in 2023 alone. It's a structural feature of public mempools, not a patch-able bug.
Stage 3: Execution — Reentrancy
Your transaction made it through. Now it's at the mercy of whoever wrote the contract.
Re-entrancy is one of the oldest and most expensive vulnerabilities in smart contract history! It's what took down The DAO in 2016 for $60 million. The core idea is that a contract sends ETH to an external address before updating its own internal balance. A malicious contract can intercept that ETH transfer, immediately call back into the original function, and drain it again all before the first withdrawal finishes recording.
Back to the vending machine analogy from last post, you ask for a refund, the machine starts dispensing your dollar, but before it logs the transaction, you trigger another refund. And another. The machine empties out while its ledger still thinks you have a full balance.
The fix is straightforward — update state before making external calls, not after. But auditors still find reentrancy vulnerabilities in production contracts regularly. Simple patterns, repeated mistakes, millions of dollars lost.
One Pattern Across All Three
What's interesting about all three attacks is that none of them break cryptography. The signature math is fine. The consensus mechanism is fine. The chain is doing exactly what it's supposed to.
What breaks is the layer around it — user interfaces, mempool visibility, contract logic. The protocol is secure. Everything built on top of it is fair game.
That's the auditor's job: everything between "the user clicks confirm" and "the chain records the result."
That's it for this post. Hope you learnt something and thanks for reading. See you next time!
